The ErbB/HER subfamily of polypeptide growth factor receptors include the epidermal growth factor (EGF) receptor (EGFR, ErbB1/HER1), the neu oncogene product (ErbB2/HER2), and the more recently identified ErbB3/HER3 and ErbB4/HER4 receptor proteins (see, e.g., Hynes et. al. (1994) Biochim. Biophys. Acta Rev. Cancer 1198, 165-184). Each of these receptors is predicted to consist of an extracellular ligand-binding domain, a membrane-spanning domain, a cytosolic protein tyrosine kinase (PTK) domain and a C-terminal phosphorylation domain (see, e.g., Kim et al., (1998) Biochem. J. 334, 189-195).
Experiments in vitro have indicated that the protein tyrosine kinase activity of the ErbB3 protein is attenuated significantly relative to that of other ErbB/HER family members and this attenuation has been attributed, in part, to the occurrence of non-conservative amino acid substitutions in the predicted catalytic domain of ErbB3 (see, e.g., Guy et al. (1994) Proc. Natl. Acad. Sci. USA. 91, 8132-8136; Sierke et al. (1997) Biochem. J. 322, 757-763). However, the ErbB3 protein has been shown to be phosphorylated in a variety of cellular contexts. For example, ErbB3 is constitutively phosphorylated on tyrosine residues in a subset of human breast cancer cell lines overexpressing this protein (see, e.g., Kraus et al. (1993) Proc. Natl. Acad. Sci. USA. 90, 2900-2904; and Kim et al. Supra; see, also, Schaefer et al. (2006) Neoplasia 8(7):613-22 and Schaefer et al. Cancer Res (2004) 64(10):3395-405).
Although, the role of ErbB3 in cancer has been explored (see, e.g., Horst et al. (2005) 115, 519-527; Xue et al. (2006) Cancer Res. 66, 1418-1426), ErbB3 remains largely unappreciated as a target for clinical intervention. Current immunotherapies primarily focus on inhibiting the action of ErbB2 and, in particular, heterodimerization of ErbB2/ErbB3 complexes (see, e.g., Sliwkowski et al. (1994) J. Biol. Chem. 269(20):14661-14665 (1994)). Accordingly, it is an object of the present invention to provide improved immunotherapies that effectively inhibit ErbB3 signaling, and can be used to treat and diagnose a variety of cancers.